Guillain-Barré syndrome in Larimer County, Colorado: a high-incidence area.

During the period 1981-1983, 19 cases of Guillain-Barré syndrome (GBS) occurred in residents of Larimer County, Colorado, for an incidence of 4.0 cases per 100,000 population per year, compared with 1.2 cases per 100,000 per year in 1975-1980 (p less than 0.05). The higher incidence of GBS in 1981-1983 may represent an unusual chance occurrence, since no patient characteristics or predisposing events could be found to explain the increase. Nevertheless, the findings demonstrate that over a period of as long as 3 years, the crude average annual incidence of GBS in a large, well-defined population may exceed by twofold the upper limit of the previously reported range (0.6 to 1.9 cases per 100,000 per year).